A. Field of the Invention
The present invention relates to a color digital imaging apparatus, especially to a color digital imaging apparatus having a rule-based hue-shift processor for after-shot recovery.
B. Description of the Prior Art
As color digital imaging apparatus, such as digital cameras and color video cameras, are getting more popular in the market, the demand for better color performance of the output images is also increasing. Since a slight color difference between an output image and an actual scene is noticeable, therefore the effects of the color reproduction in the output image will determine the quality of the color digital imaging devices.
For color reproduction, it is desirable to select all optimum set of spectral characteristics for the color sensors, such as CCD (Charge Coupled Device). The goal of good color reproduction is to choose a set of spectral characteristics for the color digital imaging device which is as close as possible to the spectral characteristics of the intended display device. The digital signals produced by the color sensor will be a function of the spectral characteristics of the light used to illuminate the scene. For example, if the color processing in a camera is designed to give good color reproduction in a daylight light source, unacceptable color reproduction may be obtained if the camera is used with, flash, or fluorescent illumination. This is due to the fact that the response measured by the color sensors is a function of the spectral power distribution of the light source as well as the spectral reflection of the objects in the scene, and the spectral responses of the sensors.
To improve the color performance of a color digital imaging device, a conventional technology uses a color-correction matrix in the pre-processing section of the color digital imaging device. The matrix coefficient is obtained from a color matching function. Usually the color matching function is obtained via complicated numerical analysis of the images. Some conventional technology applies a color temperature detecting circuit in the pre-processing section for modifying the matrix coefficients for a primary color separator used to perform a color-correction operation for a color digital imaging device. Eventually, selecting the color-correction matrix coefficients can account for changes in illuminant color temperature and provide an output image with better color performance.
Conventional color digital imaging devices also require a post-processing module for processing the downloaded images. Usually, the post-processing module are designed following the ICC (International Color Consortium) Profile Format Specification for defining the output format of colors and also recording the conversion profiles of the spectral characteristics of a particular light source. Accordingly, the RGB input profiles are established which will correct the spectral sensitivities of an input device for a connection space. Thereupon, the output profiles are used to convert the signals from the connection space to a format that is expected by an output device. The implementation for the conventional technology is very complicated. The manufacture cost is also very high.
Accordingly, it is an object of the present invention to provide a color digital imaging apparatus having a rule-based hue-shift processor which can provide a color correction parameter for a color transfer function according to the hue-shift analysis on an original color digital image, thereby to generate good color reproduction of images without the requirement of complicated numerical analysis.
It is another object of the present invention to provide an intelligent color digital imaging apparatus capable of after-shot recovery. The user can manually select a correspondent light source at the time of taking pictures, or even in viewing the images displayed on the display device. The after-shot recovery function is performed by a rule-based hue-shift processor for generating a color correction parameter to adjust the hue of the captured image according to a correct light source selected at a computer system. Consequently, the quality of the output image can be further guaranteed even after shot.
In accordance with the present invention, the color digital imaging apparatus is embodied with a light source selector for generating an illumination selecting signal selected by the user. The after-shot recovery function is implemented in a computer system. When downloading the captured image in a computer system, a color correction function is performed at the computer system. The color correction function is mainly performed by the following elements: hue-shift analyzer for performing hue analysis on the original color digital image signals and generating hue-shift parameters; a Rule-Based hue-shift processor for generating color correction parameters by triggering a set of predetermined rules in response to the illumination selecting signal and the hue-shift parameters; a color correction module for performing color correction on the original digital color image signals and generating corrected digital color image signals according to a color conversion function based on the color correction parameters; a memory for storing the hue-shift parameters and the corrected digital color image signals; and a display interface for transferring the corrected digital color image signals from the second memory means to a display device and displaying a dialog box for illumination condition selections.